This invention relates to multiple input data processing systems, and in particular to means for insuring that all events received by such a system are processed in order of their time of arrival.
In guidance systems, events are generated by accelerometers, usually signifying the passing of a delta-velocity increment (.DELTA.V) in each of three coordinates (X, Y, Z) for forward and reverse direction (+, -). Similar events are generated by torquing commands. In order to assure that the measurement system is functioning correctly, a positive and a negative event, alternating at precisely 500 milliseconds is provided as a reference. This adds up to fourteen events that have to be measured.
The processing of an event, i.e., reading the time of occurrence from a precision clock, registering the identity, and eventually recording the information on digital tape tape for further computer use, takes a certain amount of time. With a single processing line no other event can be accepted during this time (lock-out time).
Transmission noise not only affects the proper occurrence of an event, it also creates entirely new events that are in no way related to the intended signal. Even though there is a limit in the system of how close the events on a line can follow each other, a noise spike might occur just ahead of a legitimate event and will lock it out. Unless the legitimate event can also be accepted, noise that close would have to be interpreted as the desired event.
Even with a system that employs multiple processing lines, e.g., one for each input, there still is a lock-out for each individual line and the noise problem is not solved. Because the occurrence of events is random as far as the processing system is concerned, i.e., no particular input line can be given priority, the sequence of arrivals has to be maintained for processing. This is not possible with fixed scan programs or software priority interrupt schemes and therefore the lock-out time for an individual input may be multiplied by the number of later arrivals processed ahead of it.
The present invention is directed toward overcoming the limitations of prior art systems in these regards by means of random action event switching techniques that are especially designed to solve the problem of measuring the occurrences of several simultaneous and near-simultaneous events.